In recent years, an organic photoconductor (OPC) has replaced an inorganic photoconductor, and has been commonly used for a copying machine, a facsimile, a laser printer, or a complex machine combining thereof in view of its excellent performances and various advantages. The main reasons therefore are, for example, (a) optical characteristics thereof such as a wide wavelength region and large quantity of light absorption, (b) electrical characteristics thereof such as high sensitivity and stable charging ability, (c) a wide range of selections for a material to be used, (d) easy production, (e) low cost, (f) no hazards, and the like.
In addition to the above, the diameter of the photoconductor has been more and more downsized along with the downsizing of the image forming devices, and highly resistant photoconductor has been strongly desired in view of high-speeded operation and maintenance-free for the device. From this point of view, the organic photoconductor has disadvantages such that it is generally soft as the main components of the surface layer thereof are a low molecular charge transport material and an inactive polymer, the abrasions are prone to occur due to the physical loads from the developing system or cleaning system at the time of repeated use in the process of the electrophotography. In addition, the increase in the hardness of the rubber of the cleaning blade and the increased contact pressure are necessary as the diameters of the toner particles are more and more downsized for the purpose of achieving the high image quality. These are other factors to accelerate the wearing of the photoconductor. Such the wearing of the photoconductor leads the deterioration of the sensitivity, deterioration of the electric characteristics such as lowing of the chargability, lowing of the image density, and the generation of defective images such as background depositions. Moreover, the scratches from the partially caused wearing lead images of lined depositions due to the cleaning failure. Under the current circumstances, the life-long of the photoconductor is limited as a result of this wearing or scratches, and the replacement thereof becomes necessary.
Accordingly, it is necessary to reduce the amount of the aforementioned wearing in view of the achievement of the highly durable organic photoconductor, and this is an urgent problem to be solved in this field.
As the technique which improves the abrasion resistance of the photoconductive layer, (1) the technique which uses a curable binder resin in the surface layer (for example, refer to Patent Literature 1), (2) the technique which uses a macromolecular charge transporting material (for example, refer to Patent Literature 2), and (3) the technique in which inorganic fillers are dispersed in the surface layer (for example, refer to Patent Literature 3) are proposed. Among these techniques, the technique (1) using the curable binder resin tends to increase the residual potential and thus lowers the image density due to the impurities such as unreacted residual groups, as the compatibility of the charge transporting material and the polymerization initiator is poor. Moreover, the technique (2) using the macromolecular charge transporting material and the technique (3) dispersing the inorganic fillers are capable of improving the abrasion resistance at a certain degree, but such abrasion resistance is not sufficient enough to achieve the degree required for the organic photoconductor. Furthermore, the technique (3) dispersing the inorganic fillers increases the residual potential due to the trap present on the surfaces of the inorganic fillers, and thus the image density is prone to be lowered. The techniques (1), (2) and (3) have not sufficiently achieved the total resistance including the electrical resistance and physical resistance required for the organic photoconductor.
As an alternative technique for improving the abrasion resistance of the photoconductor to the above, it has been known the technique such that a charge transporting layer is formed by using a coating liquid containing a monomer having a C—C double bond, a charge transporting material having a C—C double bond, and a binder resin (for example, refer to Patent Literature 4). The abrasion resistance and the electric characteristics are significantly improved especially by disposing, as a surface layer, a crosslinked resin layer which is formed by curing at least a tri- or more functional radical polymerizable monomer having no charge transporting structure and a radical polymerizable compound having a charge transporting structure by UV radiation (for example, refer to Patent Literatures 5, 6, and 7). In the crosslinked resin layer, three-dimensional crosslinkages are formed as a result that the coated layer of the tri- or more functional radical polymerizable monomer having no charge transporting structure and the radical polymerizable compound are irradiated with a UV light. However, if a cylindrical substrate is exposed with the UV light, the cylindrical substrate will have an extremely high temperature due to such the light energy and heat of the reaction at the time of crosslinking. Although the appropriate increase of the temperature smoothly proceed with the crosslinking reaction, the extreme increase of the temperature may lead the deterioration of the electric characteristics, and thus the temperature of the cylindrical substrate needs to be controlled.
It has been known the technical concept of the broad sense, such that a substrate for a photoconductor is cooled at the time of producing an electrophotographic photoconductor by coating various coating liquids, drying the coated films, and then curing the films. For example, Patent Literature 8 discloses that the substrate of hollow tube is cooled by externally blowing a cooled air at the time of dip-coating and drying the substrate of the photoconductor in the manufacturing process of the electrophotographic photoconductor. Patent Literature 9 discloses that the substrate drum is cooled by introducing a gas or liquid for cooling into the chuck which fix, support and moves the substrate drum while griping. Patent Literature 10 discloses that the cylindrical substrate is cooled by inserting the small cylindrical tube having the cooling water supplying tube and the cooling water releasing tube into the hollow space of the cylindrical substrate. In these conventional techniques, the problems such as the depositions from the ultra fine suspended substances generated in a cooling medium as a result of the direct contact of the cooling medium with the surface of the substrate material, time-loss caused by blast drying the wet cooling medium, the stains on the inner wall of the cylindrical tube as the marks of fine droplets, depositions of the dirt contained in the blast, and the like are not taken into consideration. Although it is presumed to achieve the good heat transfer efficiency as a result of the direct contact and the uniform cooling, however, those techniques still remains the aforementioned problems to be solved. Therefore, it has been desired to solve various problems due to the direct contact of the cooling medium, as well as achieving the uniform cooling and high efficiency of the cooling. For example, if the substrate is placed in the resting state, it may not cause an extreme defect such as a drip of the liquid, but uneven drying or curing of the coated film, or partially uneven cooling may be occur.
Patent Literature 11 discloses that the cooling device is formed from an elastic material such as a rubber, whose shape is enlarged and expanded once it is inserted inside a cylindrical substrate, and the cooling device is inserted in the cylindrical substrate, and the liquid is poured into the cooling device to thereby cool the cylindrical substrate. However, the cylindrical substrate cannot be cooled while being rotated in accordance with this method. Moreover, the elastic body is not used simply to introduce a refrigerant, but to press using a pressure control valve. The chucking part thereof is not connected with the elastic body, the temperature thereof cannot be controlled if the UV light is irradiated thereto, and the temperature of the chucking part becomes high. Moreover, Patent Literature 10 does not disclose any special consideration for the even cooling and the improvement of the cooling efficiency by uniformly contacting the elastic material to the inner wall of the cylindrical substrate in accordance with a simple method.
[Patent Literature 1] Japanese Patent Application Laid-Open (JP-A) No. 56-48637
[Patent Literature 2] Japanese Patent Application Laid-Open (JP-A) No. 64-1728
[Patent Literature 3] Japanese Patent Application Laid-Open (JP-A) No. 04-281461
[Patent Literature 4] Japanese Patent (JP-B) No. 3194392
[Patent Literature 5] Japanese Patent Application Laid-Open (JP-A) No. 2004-302450
[Patent Literature 6] Japanese Patent Application Laid-Open (JP-A) No. 2004-302451
[Patent Literature 7] Japanese Patent Application Laid-Open (JP-A) No. 2004-302452
[Patent Literature 8] Japanese Patent Application Laid-Open (JP-A) No. 2006-255679
[Patent Literature 9] Japanese Patent Application Laid-Open (JP-A) No. 63-77061
[Patent Literature 10] Japanese Patent Application Laid-Open (JP-A) No. 08-15876
[Patent Literature 11] Japanese Patent (JP-B) No. 3154263